Squirrel-cage rotor for asynchronous motors
A squirrel-cage rotor for asynchronous motors is provided with a lamination stack made of a magnetic material and a plurality of bars, the intermediate portions of which engage respective slots of the lamination stack; the end portions of the bars protrude with respect to the lamination stack at both axial ends of the rotor and are fixed to two shorting rings; a plurality of spaces are defined, axially, by the lamination stack and the shorting rings, and tangentially by the end portions of the bars; part of such spaces is engaged by stiffening blocks arranged in contact with the end portions of the adjacent bars.
1. A squirrel-cage rotor for asynchronous motors, comprising:
a lamination stack made of magnetic material defining a plurality of slots;
a cage comprising:
a) a plurality of bars having intermediate portions that engage said slots, and opposing end portions that protrude with respect to said lamination stack;
b) two shorting rings fixed to said end portions;
a plurality of spaces defined, axially, by said lamination stack and said shorting rings, and tangentially by said end portions;
wherein some of said spaces are engaged by stiffening blocks, each stiffening block being in contact with the end portions of both the adjacent bars; the number, the positions and the dimensions of said stiffening blocks being defined so as to increase at least the first torsional eigenfrequency of the rotor to a value higher than the first harmonic frequency of the torque oscillations.
2. The rotor according to claim 1 , wherein said stiffening blocks are fixed directly to the end portions of the adjacent bars.
3. The rotor according to claim 2 , wherein said stiffening blocks are welded to said end portions.
4. The rotor according to claim 2 , wherein said stiffening blocks are glued to said end portions.
5. The rotor according to claim 1 , wherein, in each axial end of the rotor, said stiffening blocks are arranged at an equal distance from one another about the axis of the rotor.
6. The rotor according to claim 1 , wherein, in each axial end of the rotor, said stiffening blocks have the same shape, the same dimensions, and the same positions in the respective spaces.
7. The rotor according to claim 1 , wherein said stiffening blocks are arranged axially in a central position between said lamination stack and the shorting ring.
8. The rotor according to claim 1 , wherein said stiffening blocks are arranged in contact with the shorting ring.
9. The rotor according to claim 8 , wherein said stiffening blocks are made in one-piece with the shorting ring.
10. The rotor according to claim 1 , wherein the number of said stiffening blocks proportional to the pole pairs of the motor.
11. The rotor according to claim 1 , wherein said stiffening blocks are made of an electric insulator material.
12. The rotor according to claim 1 , wherein said stiffening blocks are made of copper.
13. The rotor according to claim 1 , wherein said stiffening blocks are parallelepiped in shape.
14. The rotor according to claim 1 , wherein said stiffening blocks are delimited axially by concave surfaces.